they will look at security and how four americans, including ambassador chris stevens, were killed in an attack on the anniversary of september 11. american airlines discovers why some of its seats came loose. u.s. soldiers are on the lookout for afghan allies who may be enemies. and why half of the great barrier reef has vanished. when the "cbs evening news" continues. >> pelley: two u.s. border patrol agents came under fire early this morning along the mexican border and agent nicholas ivy was killed. his partner was wounded. they were on patrol in arizona, the shooter or shooters got away. the agents were assigned to a border patrol station recently named after agent brian terry who was killed in a shoot-out with drug dealers two years ago. next sunday will mark 11 years since the u.s. went to war in afghanistan. the second-longest war in u.s. history behind vietnam. the plan for getting american troops out depends on training afghan soldiers to do the fighting against taliban themselves but there have been setbacks lately as some of the trainees have turned their guns on their u.s